That Giant is one beautiful bike. If you don't want to measure it yourself, I suggest bringing it to a LBS to find out the size, but all that's required is a tape measure running from the center of the bottom bracket to the top of top tube, then top of seat tube (not post). I gave you two methods because both have been used by different manufacturers. By taking both, you may be able to narrow down the size.

I just took a quick look at the Sette frame, but I did notice that you're going to have a problem carrying over the downtube shifters on the Giant because the Sette has cable stops rather than bosses, which is predictable seeing as most buyers will run STI shifters. But the larger problem is going to be carrying over the 7 spd freewheel because it's difficult to upgrade (to 8,9,10) from there without swapping out a number of parts. Most often, it's not worth it.

Honestly, that's such a nice frame that I think you should bring it to your LBS and see if they can taylor the fit for you. It's possible that you're close in sizing and a knowledgeable fitter may be able to position you better on the bike, but I'm guessing. If it's sized wrong for you, there's no way to get a good fit.

I just took a quick look at the Sette frame, but I did notice that you're going to have a problem carrying over the downtube shifters on the Giant because the Sette has cable stops rather than bosses, which is predictable seeing as most buyers will run STI shifters. But the larger problem is going to be carrying over the 7 spd freewheel because it's difficult to upgrade (to 8,9,10) from there without swapping out a number of parts. Most often, it's not worth it.

I think he could go with bar end shifters and use the rest of the components. Correct me if I'm wrong.

I think he could go with bar end shifters and use the rest of the components. Correct me if I'm wrong.

No, you're right. That would be an option. I was thinking too literally about swapping parts over rather than changing them. I still think the 7 spd is going to pose a problem for any future upgrades, though. I'd be more tempted to leave the bike 'as is' (period correct) and either attempt a fitting and if unsuccessful, sell it.

just stood over the bike, seems to be about a solid 2 inches between top tube and dangerous places.
I measured the top tube from the head post to the seat post and it was right on 20inches.
I measure the vertical tube from the crank joint to the where the seat post enters frame. 20inches.

That being said, if I can find a seat post with a rearward sloping angle, and a head post with a forward sweeping angle, and a little more height. I might be good, I might even be game to try some non-standard handlebars.

I am about 6 feet tall as well, but I believe I either have long torso or long arms.
How high should my knees be on the top most of the pedal stroke? How close to the front handle bars?
I think I break past parrellel to ground on thigh at top of pedal stroke and looks like knees could hit handle bars on some standing climbs.

just stood over the bike, seems to be about a solid 2 inches between top tube and dangerous places.
I measured the top tube from the head post to the seat post and it was right on 20inches.
I measure the vertical tube from the crank joint to the where the seat post enters frame. 20inches.

That being said, if I can find a seat post with a rearward sloping angle, and a head post with a forward sweeping angle, and a little more height. I might be good, I might even be game to try some non-standard handlebars.

I am about 6 feet tall as well, but I believe I either have long torso or long arms.
How high should my knees be on the top most of the pedal stroke? How close to the front handle bars?
I think I break past parrellel to ground on thigh at top of pedal stroke and looks like knees could hit handle bars on some standing climbs.

I'm going to guess that the frame is either a 50 or 51cm. Most likely too small for someone of your height. But keep in mind that I'm not seeing you on the bike and proportions do matter. If I'm close on guessing the size and you have about 2 inches clearance at the top tube, I agree that you're more long torso/ arms, shorter leg length. All that said, it might be worth a trip to your LBS for verification.

BTW, IMO that's a very good video for someone sized correctly for a frame and willing to do the initial fitting themselves.